This invention relates to producing improved high viscosity polymeric coating compositions from a low viscosity polymeric colloidal dispersion such as polymeric latex and emulsions for use in coating fabric substrates. More particularly, the invention relates to producing a high viscosity froth coating composition for coating fabric substrates such as carpet and the like by injecting a polymeric thickener emulsion into a mixing head containing a low viscosity polymeric compound with agitation to produce high viscosity froth polymeric coating composition. The invention also relates to the changing of the viscosity of the forth polymeric coating composition by varying the amount of polymeric thickener emulsion injected into the mixing head, thus allowing the use of low viscosity polymeric compounds to produce a variety of froth viscosities.
Fabric coating compositions such as aqueous froth compositions are formed by first compounding a low viscosity polymeric compound with a suitable thickener emulsion and other additives such as antioxidents, defoamers, plasticizers, fillers, extenders, froth aids, and the like, in a compounding tank and then passing the compounded polymeric composition through a conduit pipe to a high speed mixing head located adjacent to a coating apparatus. Air is introduced into the composition immediately before its passage into the mixing head so that proper frothing is accomplished in the mixing head.
In the mixing head, the polymeric composition is thoroughly mixed by high speed agitation to froth the polymeric composition which, due to the presence of thickener added in the compounding tank, is of a higher viscosity than the viscosity of the polymeric compound. The froth polymeric composition exiting from the mixing head is immediately conveyed to a pan for roller application of the froth over the surface of a substrate to deposit a uniform coating of the new frothed polymeric composition.
The stability of the froth and the control of the size of bubbles formed by frothing are related to the degree of increase in viscosity which can be produced, which of course is dependent on the amount of thickener emulsion that is mixed in the low viscosity polymer compound during the compounding operation. The amount of thickener emulsion that can be incorporated into the polymeric coating composition is limited by the requirement for adequate flow of the compound polymeric composition through the conduit pipes to the mixing head located near or adjacent to the coating mechanism. The action of the thickener increases the viscosity of the compounded polymer composition making it more resistant to conduit flow. Thus, if too much thickener is added in an effort to increase the viscosity of the froth polymeric composition exiting from the mixing head, the resistance to flow will become so great that the flow of the polymeric composition to the mixing head will not be adequate for practical production use.
Since the total amount of thickener used is an inherent part of the initial compounding of the polymeric composition, its viscosity is predetermined before it enters the mixing head. Because of the fixed viscosity of the froth polymeric coating composition, it can be used for one type of coating. Thus, if there is a change of substrate or other conditions requiring a different viscosity of the froth composition, a new batch of polymeric composition with the required viscosity must be compounded before the change of substrate or conditions is completed. This results in increased down-time and a reduction in the amount of finished product produced. In addition, since some time is required before production normalizes after the change, significant amounts of scrap material are produced.
The closest prior art known to the Applicant is disclosed in the U.S. Pat. No. 3,825,435 to Hunt which covers a process for flocking a moving substrate material by applying a formulated mixture prepared from three separate reactants by first maintaining in separate reservoirs an acrylic adhesive, an adhesive thickening agent, and a thickening reactant with a curing catalyst. Adjustable metered quantities of material from each reservoir are brought together in a cooled mixture head and delivered from the mixing head to the surface of a moving substrate. Applicant's process differs significantly from that of Hunt supra in that a low viscosity butadiene-styrene emulsion polymeric composition is compounded with additives to form a finished low viscosity coating composition which is then passed into a high speed mixing zone where a metered amount of an acid-type thickener emulsion is injected to produce a high viscosity compound exiting from the mixing zone. The viscosity of the exiting formulation is controlled only by the amount of thickener emulsion injected into said mixing zone since no curing catalyst or thickening reactant is added.